It is often important or desirable to determine the colloid index (often referred to alternatively as the silting index or fouling index) in a liquid such as water, for example in the treatment of water. Such a method, and a suitable apparatus for carrying out the method, may be used for example for the following operations:
monitoring the degree of efficiency of the precleaning stage of a reverse osmosis installation;
monitoring reverse osmosis installations;
monitoring the quality of high-purity water after a very fine filtering stage;
monitoring filtering installations, for example sand or multi-layer filters, in water treatment, instead of measuring the degree of clouding;
monitoring boiler feed water and condensate; and
monitoring very pure water in regard to contamination due to microorganisms.
At the present time, increasing importance is being attributed to water cleaning and purification installations which operate on the principle of reverse osmosis, in the desalification of water. In such an arrangement, the water to be desalified is pressed under high pressure through membranes which are of such a nature that the molecules of water and substances contained in the water are separated. When that is done however, there is the danger that the membranes may become blocked due to particular kinds of substances in the water. This blockage effect results in losses in respect of permeability, which are irreversible, and that can cause the reverse osmosis membranes to become completely useless. Such a breakdown not only causes an interruption in operation of the equipment, but also increases the operating cost thereof as the membranes are relatively expensive items.